The OCS Controller requires a DataResponse object to be returned.
This means that all error handling will have to be done via exceptions
thrown and handling in the middleware.
The OCSResponse differs from other responses in that it defaults to
XML. However we fell back to json by default.
This makes sure that if nothing is set we don't pass anything.
Which defaults then to the controllers default (which is often 'json')
but in the case of the OCSResponse 'xml'.
